The invention relates to an electromagnetic actuator for a hydraulic directional control valve that can be adjusted with the electromagnetic actuator. Such directional control valves are used, for example, in internal combustion engines for controlling hydraulic camshaft adjusters.
From DE 103 00 974 A1, a proportional solenoid valve of a camshaft adjustment device for motor vehicles is known. The proportional solenoid valve has a valve housing in which a piston can be displaced and that provides several connections by which hydraulic oil can be fed. The proportional solenoid valve further comprises an electromagnet part with which the piston can be adjusted by a tappet. In one embodiment of the proportional solenoid valve, a housing of the electromagnet part is provided on the end face with a recess into which a housing of the valve part projects with one end. In the base of the recess there is an annular groove that holds a sealing ring. On the end face, the housing of the valve part contacts against this sealing ring. This seal, however, does not enable a sealing of components within the electromagnet part. Therefore, the housing of the electromagnet part must guarantee a complete seal, because otherwise hydraulic oil could leak from the electromagnet part.
DE 10 2005 048 732 A1 relates to an electromagnetic actuator of a hydraulic directional control valve. FIG. 1 of DE 10 2005 048 732 A1, which is incorporated into this application as FIG. 1A, shows the arrangement of an inner rotor 42 and a hydraulic directional control valve 44 of a camshaft adjuster 40. The electromagnetic actuator comprises an armature that is arranged within an armature space so that it can move axially and a pole core that is arranged in a receptacle and the armature space is limited in one movement direction of the armature. Furthermore, the electromagnetic actuator comprises a coil that is preferably extrusion coated with a non-magnetizable material, so that a coil body is formed. The coil body has a hollow cylindrical base shape that fits in a positive fit connection in a housing of the electromagnetic actuator. The housing does not completely enclose the components of the hydraulic directional control valve, whereby a sealing element is needed between the coil body and the housing. A disadvantage in this solution is that the introduction of the seal is complicated for the assembly of the electromagnetic actuator, in order to guarantee, in particular, a long-term function.
DE 101 53 019 A1 shows an electromagnet that is suitable, in particular, as a proportional magnet for activating a hydraulic valve. The electromagnet comprises a hollow cylindrical coil body that is bounded by an upper pole shoe and a lower pole shoe. The electromagnet is enclosed by a magnetic housing. The coil body acts magnetically on a magnetic armature that forwards the magnetic force via a tappet rod for activating the hydraulic valve. The coil body is sealed relative to the hydraulic valve first by a non-magnetizable metal tube, wherein, however, another seal is needed via a housing of the proportional magnet.
A solution known from the state of the art for sealing a coil body relative to a not completely enclosed housing of an electromagnetic actuator is provided in that the seal is constructed as a liquid seal. Such liquid seals, however, are subjected to strong processing fluctuations as a function of, for example, the air humidity, the working life, the temperature, or the chemical changes during processing interruptions, so that a reliable function of the liquid seal can be guaranteed only with high expense.
DE 10 2005 048 732 A1 relates to an electromagnetic actuator of a hydraulic directional control valve. The electromagnetic actuator comprises an armature that is arranged within an armature space so that it can move axially and a pole core that is arranged in a receptacle and the armature space is limited in one movement direction of the armature. Furthermore, the electromagnetic actuator comprises a coil that is preferably extrusion coated with a non-magnetizable material, so that a coil body is formed. The coil body has a hollow cylindrical base shape that fits in a positive fit connection in a housing of the electromagnetic actuator. The housing does not completely enclose the components of the hydraulic directional control valve, whereby a sealing element is needed between the coil body and the housing. A disadvantage in this solution is that the introduction of the seal is complicated for the assembly of the electromagnetic actuator, in order to guarantee, in particular, a long-term function.
FIG. 1 shows another electromagnetic actuator according to the state of the art in a cross-sectional view. This electromagnetic actuator is constructed for adjusting a hydraulic directional control valve that is formed as a central valve and that is arranged radially within an internal rotor of a device for the variable adjustment of the control times of an internal combustion engine. The electromagnetic actuator initially comprises a coil 01 that is fed electrically via a plug-in contact 02. The coil 01 is arranged within a coil body 03 that is formed, for example, by an assembled and bonded housing or that is finished by extrusion coating of the coil 01 with a plastic. The magnetic field that can be generated with the coil 01 is transmitted to a movable magnetic armature 09 by a soft iron circuit that is made from a yoke 04, a yoke plate 06, a pole core 07, and a housing 08. The magnetic field exerts a magnetic force on the magnetic armature 09 across an air gap between the pole core 07 and the magnetic armature 09. This magnetic force is transmitted via a pressure pin 11 on a piston of the central valve (not shown). The electromagnetic actuator is mounted by a flange 12 of the housing 08 on the central valve or on a housing surrounding the central valve. Hydraulic oil is forced from the hydraulic directional control valve formed as a central valve through the housing 08 into the region of the magnetic armature 09. Because the electromagnetic actuator is not completely surrounded by the housing 08, it requires a seal 13 between the coil body 03 and the housing 08. The seal 13 is constructed as a planar piece seal, for example, in the form of an O-ring or a profiled sealing ring that is introduced into a groove in the coil body 03. The material cross section of the seal 13 is significantly smaller than the diameter of its annular shape. Due to this relationship, the seal 13 is taken to be mechanically unstable, so that during the assembly of the coil body 03 in the housing 08, the seal 13 can emerge partially or completely from the groove in the coil body 03, whereby the assembly is susceptible to failure.